In any network, a customer always hopes to implement service transmission over the network quickly and with high quality. The case is true as for an NGN. The NGN is an integrated network, which integrates fixed communication with mobile communication by using packet technologies, such as IP technologies, as the bearer network technologies, and carries various telecommunication services such as voice, image and data over IP connections between communication entities. At present, service reachability arises as a requirement for the NGN, which requires that a customer can obtain his or her subscribed NGN services on demand no matter which access technology the NGN applies.
For implementing the service reachability, the signaling flow of the NGN services should be ensured to be straightway at any moment and be transmitted reliably. In an IP access network of the NGN, all IP packets issued by customers are transmitted forward with a best-effort mode or a priority mode, and the signaling flow and the media flow of the NGN services are mixed in transmission. Since the network resources are always limited, when any segment or any node of the network between a customer and a service control function entity is fully-loaded or congested, the signaling flow of the NGN services, which contains a service request signaling packet of the customer, may be discarded and unable to reach the service control function entity. As a result, even if the customer requests services of a relatively higher priority, it is possible that no answer will be received and the service reachability fails to be implemented.
Moreover, in the case of mixing the signaling flow and the media flow of the NGN services in transmission, it is difficult for an IP network transmission node to identify whether the transmitted packet is a signaling flow packet or a media flow packet, and to guarantee that the signaling flow packet of the NGN services is not discarded in the case of the congestion, which makes it obviously impossible to implement the service reachability in this case.
The service requested by a customer may also be an emergent call service with a top priority such as a burglar alarm call, a fire alarm call, a traffic alarm call or a first aid call, which use uniform numbers as well known in public and require a round-the-clock straightway connection; and each telephone customer has the right to dial such emergent numbers for seeking help. Such a service requires not only that the signaling flow of service can always be transmitted straightway and reliably, but also that the media flow of service can be established on demand and be transmitted reliably. If a signaling flow is unable to reach a service control entity reliably, it is impossible to establish an application session and start a media flow, say nothing of supporting an emergent call service and guaranteeing the Quality of Service (QoS) of the media flow transmission.
Besides, for solving such problems as address, security and QoS, there may be deployed security devices such as a Net Address Translation (NAT) device and a firewall device in an NGN bearer network; there may also be deployed admission control implemented by a service control entity for the media flow. Due to the variety of service signaling protocol, it should be simple and reliable to guarantee that an NGN service signaling flow is able to pass through these security devices and eventually reach the service control entity. If the NGN service signaling flow is unable to reach the service control entity, it is impossible to trigger the admission control for the media flow by means of a service request.
Major problems of the NGN have been described, and other problems of the currently-built NGN will be described as follows.
The currently-built NGN mainly focuses on packets of voice services; it carries a voice service over an IP physical private network, and still carries a data service over the original Internet network. In other words, a conventional telephone terminal is still connected to a voice network gateway device over the common telephone line, and a computer device is connected to a broadband access server over the Digital Subscriber Line (xDSL) and the Ethernet. As a result, a voice service and a data service are separated from each other from the customer terminal, and the IP private network as the bearer network of the voice service guarantees sufficient redundancy resources to avoid the congestion, thus the transmission reliability of the signaling flow and the media flow of the voice service is guaranteed. Therefore, this IP private network scheme for NGN voice services not only guarantees the customer reachability of the NGN voice services, but also supports emergent call services.
Though the above IP private network scheme for the NGN voice services guarantees the transmission of voice service, the final objective of the NGN is to carry over one all-IP network all NGN services, i.e. all IP value-added service consisting of voice services, video services and data services. Along with the enrichment of NGN service types, the percentage of all NGN services occupied by the voice services is very small and gradually decreases, so that operators need to consider the transmission performance of other services. If all NGN services are carried over the IP physical private network, the following drawbacks will occur.
1) The cost of operation and maintenance of IP physical private network is very high, which makes the cost of operation and maintenance of the NGN very high;
2) Each IP private network needs to set a certain amount of resource redundancy, which makes the redundancy waste of the entire NGN resources very severe; and
3) Because different services are transmitted by a respective private network, it is impossible to provide multimedia terminal customers with integrated IP multicast services, and the IP private network is unable to guarantee the transmission quality of service at present.
The current NGN scheme has another trend that the NGN access network and the NGN core network are gradually utilizing IP technology. In an all-IP bearer network, a common interface between a customer and the network utilizes the IP technology, and the end-to-end transmission of voice, video and data services is implemented by means of the IP technology. Essentially, an NGN service refers to as an operative and administrable IP value-added service of the telecom level. To guarantee the real-time performance of the NGN services and the QoS of services with a high priority, it is possible to logically partition the IP network resources with a preset configuration mode; different logic parts carry different services. For example, voice, video and data services are isolated in the access network and the core network, and are respectively provided with reserved resources. These services may be isolated and provided with respective reserved resources by means of the Permanent Virtual Circuit (PVC) technology or the Virtual Local Area Network (VLAN) technology in the access network and by means of the Multi-Protocol Label Switching (MPLS) technology or the Virtual Private Network (VPN) technology in the core network. The admission control is performed at the ingress of network edge, and different service media flows are labeled with different forward priorities and discard priorities for forward transmission. With this configuration, it is possible to guarantee that the routing and resources occupation of different service types do not interfere with each other.
The signaling flow and the media flow are still transmitted in a mixed way in the logical network according to the NGN scheme, and only the signaling and the media flows of the service with the highest priority are guaranteed to be transmitted straightway and reliably in any case of resource occupancy rate. Though the resources are separately reserved for the signaling flow, the logical bearer network is partitioned and the resources are reserved only for the signaling flowing of the NGN voice services, and the signaling flow isolation associated with other NGN services is not considered uniformly. In practice, a telecommunication operator should guarantee that the signaling flows of all NGN services presubscribed by a customer are transmitted straightway and reliably no matter which service level or service type the service is of. It has not been recognized that guaranteeing the service reachability, i.e. the straightway and reliable transmission of signaling flow of all telecom-level services in any case of resource occupancy rate, is of the most importance for all telecom-level services in the discussion of the QoS problem of the NGN. It, however, has not been recognized either that the straightway and reliable transmission of signaling flow of all telecom-level services in any case of resource occupancy rate is the chief condition for triggering the NGN resource and admission control function entity to work and supporting an emergent call service in the NGN.
In particular, though the latter NGN scheme guarantees the service QoS within the planning range of traffic by means of the reserved resources, and improves the network resource efficiency beyond the IP private network scheme, it still has the following drawbacks.
1) Because the signaling flows and the media flows of the NGN service are still mixed while being transmitted in the logical network, it is also difficult to guarantee the straightway and reliable transmission of signaling flows of the service with a relative low priority and signaling flows of the free best-effort service in any case of resource occupation rate, and it is difficult to guarantee the service reachability of the service with the relative low priority and the best-effort service, which makes it difficult to guarantee the service request triggers the admission control for the media flow.
2) When the signaling flow is transmitted straightway, the resource reserved for high priority services may be occupied by the free best-effort service instead of the service with a relative low priority, which causes a resource-inversion condition. In other words, when the network has free resources, the service with the relative low priority is unable to get resource while the free best-effort may obtain the resource which may be grabbed by the service with a high priority.
3) It is impossible to improve the capability of anti-delay, anti-jitter and anti-packet-lost of the media flow.
To sum up, the current NGN scheme is unable to guarantee that signaling flows of all NGN services are transmitted straightway and reliably, which makes it difficult to implement the service reachability. The signaling flow of the NGN service is unable to reach the service control entity, so that the media flow can not be transmitted, which makes it difficult to implement an emergent call service and trigger the admission control for the media flow.